Just how good are those used, sealed lead-acid batteries? [RE-wrenches]

Jeff Clearwater clrwater at earthlink.net
Sat Oct 21 05:45:22 PDT 2006


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Hey Bob,

Oh yes, of course.  But the voltage and amperage curve will tell you 
all you need.

Have fun!

jc



>Thanks, Jeff.  Note, however, that, because these are sealed 
>batteries, I will be unable to measure SG.
>
>Bob Clark
>SolarWind Energy Systems, LLC
>bclark at solar-wind.us<mailto:bclark at solar-wind.us>
>   ----- Original Message -----
>   From: Jeff Clearwater<mailto:clrwater at earthlink.net>
>   To: RE-wrenches at topica.com<mailto:RE-wrenches at topica.com>
>   Sent: Friday, October 20, 2006 8:59 PM
>   Subject: Re: Just how good are those used, sealed lead-acid 
>batteries? [RE-wrenches]
>
>
>
>   HI Bob,
>
>   Here's how you do it.
>
>   First understand lead acid chemistry thoroughly by reading "Battery
>   Book One" by Curtis instruments or some such book.
>
>   Then do the following procedure.
>
>   1) Set up a charging station for each battery separately (not in any
>   series and/or parallel arrangement).
>
>   2)  Bring each battery to a good equalize charge state.  For sealed
>   lead acid you want a "constant current, constant voltage, constant
>   current" type of 3 stage charge that is carefully regulated not to go
>   past the 14.4 volt or whatever the battery manufacturer recommends
>   for those batteries.
>
>   3)  Set up a load station - use a resistance element like those used
>   for dump loads.  This should be on the order of a C/10 discharge
>   rate. (i.e. if a 100 amphour battery - a 10 amp load)
>
>   4)  Now here's the tricky part that requires attention and time.
>   Discharge each battery with the load and note the start time and
>   amperage and take careful voltage and amperage and specific gravity
>   readings periodically - perhaps every 30 minutes or hour - record
>   these readings in a spreadsheet like Excel or equivalent.  Record the
>   time and voltage and amperage and SG.
>
>   5) Discharge until the battery shows about 1.90-1.95 volts/cell at
>   the C/10 rate.  (11.4 - 11.7 volta for a 12 volt battery.
>
>   6)  Graph the discharge curve you obtained - graph the voltage the
>   amperage and the specific gravity on the same graph.  Let the battery
>   sit discharged for an hour or so and take SG and voltage readings
>   again.
>
>   7)  Now you can analyze this data quick and dirty or you can analyze
>   it with sophisticated analysis.  Quick and dirty is just to take the
>   total time until you reached the state you reached times the amperage
>   during that time (rough average) and that will give you rough
>   amphours that the battery delivered to that theoretical state of
>   charge.  You can obtain State of Charge vs SG readings for  your
>   particular battery from the manufacturer.  By comparing the
>   theoretical new battery graph to yours you can roughly determine how
>   much capacity yours has.  This will also give you the relative health
>   of each battery.
>
>   A more sophisticated analysis might involve you integrating the area
>   of the time vs amperage or time vs. SG curve and determining exact
>   amphours.  But you can tell alot if you just compare your curves to
>   that of a new battery or the manufacturer's curves or even just to
>   each other.
>
>   Oh yea - then charge the batteries back up - don't let them sit discharged!
>
>   You may have to do this procedure a few times - especially if the
>   batteries have been sitting around - they may need "working" to get
>   to accept a fuller charge.
>
>   AND you need to assess whether all this labor is worth the price of
>   these batteries!  Most VRLA batteries don't last more than 200-300
>   cycles max.
>
>   Hope that helps!
>
>   Best,
>
>   Jeff Clearwater
>   Village Power Design
>
>
>   >Wrenches:
>   >
>   >I can quite easily measure the voltage of a sealed battery by using
>   >a meter, but how do I know how "good" a used, sealed battery is?
>   >That is, if the sealed, lead-acid battery has been in use for 2 to 3
>   >years, how do I determine its condition (and capacity to hold a
>   >charge) if I do not know its use history?  I need to determine how
>   >"good" each of 20 of these batteries are (I have reason to believe
>   >that the condition of these batteries varies widely).  I would hate
>   >to have to haul them somewhere (except to recycle them if they are
>   >no good) to be tested.
>   >
>   >Bob Clark
>   >SolarWind Energy Systems, LLC
> 
>>bclark at solar-wind.us<mailto:bclark at solar-wind.us<mailto:bclark at solar-wind.us>>
>   >[Non-text portions of this message have been removed]
>   >
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>   --
>   ~~~~~~~~~~~~~
>   Jeff Clearwater
>   Village Power Design
>   Sustainable Energy & Water Solutions for Home & Village
>   http://www.villagepower.com<http://www.villagepower.com/>
>   gosolar at villagepower.com<mailto:gosolar at villagepower.com>
>   NABCEP (tm) Certified Solar PV Installer
>
>   530-470-9166
>   877-SOLARVillage
>   877-765-2784
>   65 Schoolhouse Rd
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-- 
~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design
Sustainable Energy & Water Solutions for Home & Village
http://www.villagepower.com
gosolar at villagepower.com
NABCEP (tm) Certified Solar PV Installer

530-470-9166
877-SOLARVillage
877-765-2784
65 Schoolhouse Rd
Amherst, MA 01002
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~


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